1. Field of the Invention
The invention relates to a method as well as a network element such as a name server, a gateway device and a mobile node by which a global reachability in communication networks can be achieved.
2. Description of the Related Art
Host reachability is an essential function in all networks and especially in the mobile networks. Location updates are integral part of any the reachability solution—whenever a host changes its location in the network, namely its IP (Internet Protocol) address, its reachability information needs to be updated.
However, it is a very rare occasion, if not non-existent, that an IP packet is sent without payload carrying transport layer header and some application data. This means that host reachability itself is not sufficient for end user's communication needs, but also service reachability needs to be considered. In other words, in the case of host reachability it is actually a service in the specific host, the peer is trying to reach, not just the host.
Services/applications are identified on transport layer via port numbers, e.g. HTTP (HyperText Transfer Protocol) uses typically port number 80 or 8080. When port mapping is not happening on the packet route (typical in public IP domain), it is enough for service reachability to get only the host's locator information (IP address), because the port numbers that the applications use have no role in packet forwarding. Locator information in this case is typically retrieved from a DNS (domain name system) framework by using A type query (domain name→IP address mapping). Therefore, the term host reachability is used, because location of the service in host is well-known via service specific port number.
The situation is different when port mapping happens on the packet route (typical case in the NA(P)T (network address (port) translation) box). Port mapping means that applications in the connecting peer can no longer reach services provided by the host behind the NA(P)T by using well-known service port numbers, because of the common NA(P)T traversal mechanism, where connections are mapped in NA(P)T with (NA(P)T IP, port number) pair.
Moreover, the existence of a NA(P)T is a sign of the fact that the network behind it is having a private address space, which means that the host located there cannot be reached trivially by using public domain scenario methods. Namely, private IP addresses are not routable in the public domain.
At present, domain name system (DNS) is only available globally viable framework that can provide reachability for an IP host.
The current IPv4 based Internet is running short of addresses. More and more addresses are required due to, for example, mobile nodes are becoming IP nodes in the next generation of mobile networks. Also, countries like China and India are in the middle of Internet revolution and require addresses.
Evidently, IPv6 is long-term solution to address shortage, but coming of IPv6 is still somewhere in the future. To tackle the issue, quicker several middle-box solution have been developed. In these solutions, networks are divided into one public Internet and innumerous private networks that share same address spaces. NA(P)T is the most widely used middle-box solution.
Private networks behind middle-boxes, like NA(P)T, have one major problem: hosts connected to these networks are not reachable from the public network. That is, the host itself must initiate all connections. This has been somewhat acceptable in the past where application have been mainly of a client-server type, and a client always initiates the service request. However, the reachability issue is becoming more important, once peer-to-peer communication paradigm is becoming more common and this requires host (and service) reachability despite of the host location to be feasible.
There are some specific solutions defining how mobile IP can be used when MNs are located in a private address space and a home agent is located in public address space. However, there is no known prior-art generic host/service reachability solution for scenario where access network uses private IP address space.